1. Field of the Invention
The present invention is directed to a device for expelling air or gas from a sealed container through which liquid is pumped.
2. Description of the Related Art
One example of a device which includes a sealed container through which liquid is pumped is an canister-type aquarium filter.
While application of the present invention is not limited to use with canister-type aquarium filters, such filters will be used to illustrate the problem in the art solved by the present invention. As described in U.S. Pat. No. 4,601,821 to Sherman et al. entitled "Freestanding Aquarium Filter," canister-type aquarium filters include a canister containing filter media, a pump, a first hose connecting the aquarium to the canister, and a second hose connecting the pump to the aquarium. The canister also includes a removable cover which allows access to the filter media within the canister.
Typically, canister-type aquarium filters operate in the following manner. First, the pump is energized and water flows out of the pump housing, through the second hose, and into the aquarium. As water flows out of the canister, the water level within the canister decreases. The decrease in water level creates a vacuum within the canister. As used herein, the term "vacuum" refers to an area of reduced pressure. The vacuum within the canister causes water in the aquarium to be drawn into the canister through the first hose. The vacuum increases until the flow of water drawn into the canister equals the flow of water pumped out of canister. The water drawn into the canister passes through a filter media and then is drawn into the pump.
One of the major problems associated with devices which draw fluid into a sealed container is a buildup of gas within the container. In the case of canister-type aquarium filters, the presence of air within the canister often results in water noise which in turn leads to user dissatisfaction. Moreover, in those filters with the pump mounted at the top of the canister, the accumulation of gas within the canister may cause a phenomenon commonly referred to as "air lock" or "vapor lock." An "air lock" occurs when gas accumulates in the pump housing or at the entrance to the pump housing and the impeller is unable to expel the gas. Eventually, the accumulated gas will prevent water from entering the pump housing and, accordingly, the pump (and filter) will malfunction.
The buildup of gas within the container may be the result of air bubbles and other dissolved gasses present in the fluid. As a variety of devices are used to aerate the water in an aquarium, air bubbles and dissolved gasses are especially prevalent in the water drawn into canister-type aquarium filters. Once inside the canister, the bubbles expand due to the vacuum within the canister and aggregate on the filter media to form larger bubbles. The larger bubbles eventually release from the aggregating surfaces and rise to the top of the canister.
Additionally, the buildup of gas within the container may be caused by gas leaking into the container at the seal between the cover and the canister. Such leaks are caused by the vacuum within the canister which draws gas into the canister. The vacuum is greatest when the container is located near or above the level of the reservoir from which the fluid is drawn. Accordingly, gas leaks into the container will be especially prevalent when the container is located at or above the reservoir level.